Method and apparatus for explosive drilling utilizing spark pumps for detonating explosives

ABSTRACT

This specification discloses combination rotary and explosive drilling methods and apparatus for drilling wellbores. Explosive charges are pumped down a drill pipe along with circulating drilling fluid and seated in a seat within a drilling tool located at the lower end of the drill pipe. The explosive charges are then detonated by means of a spark pump. The lower portion of the drilling tool is shaped as a reflector or concentrator which functions to concentrate the energy of the explosion to fragment earth formations below the drilling tool. The drill pipe is rotated, thereby rotating cutting means attached to the lower portion of the drilling tool which also fragments the earth formations below the drilling tool and keeps the wellbore in gauge. Circulating drilling fluid removes the fragmented earth formations to the surface.

Unite States Patent [72] Inventor Frank A. Angona Dallas, Tex. [21] Appl. No. 855,877 22 Filed Sept. 8, 1969 [45] Patented Apr. 27, 1971 [73] Assignee Mobil Oil Corporation [54] METHOD AND APPARATUS FOR EXPLOSIVE DRILLING UTILIZING SPARK PUMPS FOR DETONATING EXPLOSIVES 10 Claims, 3 Drawing Figs.

[52] US. Cl 175/4.S, l 75/ 4.54 [51] Int. Cl E2lb 7/00, E21c 19/00 [50] Field of Search 175/2, 3.5, 45,454; 102/21.6

[56] References Cited UNITED STATES PATENTS 3,070,010 12/1962 Robinson l75/4.5 3,190,372 6/1965 Johnson 175/4.5

3,274,933 9/1966 Robinsonetal. 3,491,841 1/1970 Robinson ABSTRACT: This specification discloses combination rotary and explosive drilling methods and apparatus for drilling wellbores. Explosive charges are pumped down a drill pipe along with circulating drilling fluid and seated in a seat within a drilling tool located at the lower end of the drill pipe. The explosive charges are then detonated by means of a spark pump. The lower portion of the drilling tool is shaped as a reflector or concentrator which functions to concentrate the energy of the explosion to fragment earth formations below the drilling tool. The drill pipe is rotated, thereby rotating cutting means attached to the lower portion of the drilling tool which also fragments the earth formations below the drilling tool and keeps the wellbore in gauge. Circulating drilling fluid removes the fragmented earth formations to the surface.

PATENTED APRZ? I971 SHEET 1 OF 2 FRANK A. ANGONA INVENTOR ATTORNEY Pmmen mm m 3.576.219

SHEET 2 BF 2 FRANK A. ANGONA INVENTOR ATTORNEY METHOD AND APPARATUS FOR EXPLOSIVE DRILLING UTILIZWG SPARK PUMPS FOR DETONATING EXPLOSIVES BACKGROUND OF THE INVENTION This invention relates to combination rotary and explosive drilling methods and apparatus for drilling a wellbore into earth formations. More specifically, this invention relates to methods and apparatus whereby explosive charges are detonated and the energy of the explosion concentrated to fragment earth formations.

The use of explosives in conjunction with rotary drilling for drilling a wellbore into earth formations is known in the prior art. For example, in US. Pat. No. 3,083,778, to Friedman et al., water soluble capsules containing an explosive are introduced into circulating drilling fluid. These capsules are exploded by weight imposed on the capsules by the drill bit and increased drilling rates are obtained.

The use of shaped charges in combination with nondirectional charges for drilling a wellbore into the earth is also known in the prior art. For example, in U.S. Pat. No. 3,070,010, to L. H. Robinson, Jr., an elongated shaped jet charge is carried down a well pipe by circulating drilling fluid and landed on a landing seat or nipple at or near the lower end of the well pipe. The charge is detonated responsive to differential pressure and blasts a hole in the earth at the bottom of the wellbore. A nondirectional gauging charge is then landed on the seat and extends into the hole produced by the preceding shaped jet charge. The gauging charge is detonated while tamped with drilling fluid to increase the hole size formed by the shaped charge.

It has been recognized that a substantial portion of the energy produced by the nondirectional gauging charge is directed upward and serves only to blow drilling fluid up the borehole. In US. Pat. No 3,274,933, to L. H. Robinson, Jr. et al., there is provided apparatus for directing the energy laterally of the borehole in order to more economically and effectively use the explosive material available in the explosive charge. One embodiment of Robinson et al. provides an elongated housing having a first nondirectional explosive charge at one end thereof. Positioned in the housing directly above the nondirectional explosive charge is a second nondirectional explosive charge formed generally like a cup and extending upwardly and away from the longitudinal axis of the elongated housing. Within the second charge is means for reflecting outwardly the energy produced upon detonation of the second charge. Connected to the first and second charges is means for detonating the second charge at a predetermined interval after the first charge is detonated such that the upwardly going energy produced by the first charge is deflected outwardly into the surrounding earth formation by the energy produced by the second charge.

SUMMARY OF THE INVENTION This invention concerns methods and apparatus for drilling a wellbore into earth formations with nondirectional explosive charges. In carrying out the method of this invention drilling fluid is circulated down a drill pipe within the well and up the annulus surrounding the drill pipe. Explosive charges are inserted in the circulating drilling fluid and are carried down the drill pipe and seated in seating means provided in the drilling tool. The flow of drilling fluid is thus restricted causing an increase in the pressure of the drilling fluid in the pipe. This compresses a spark pump in the drilling tool and produces electrical energy which is conducted to a first and a second electrode and detonates the explosive charge. A concentrator concentrates the energy to a focal region and fragments the earth formations. The drill pipe and drilling tool having cutting means on the lower portion thereof are rotated to cut the wellbore to gauge and the drill pipe is lowered at a rate commensurate with the rate of drilling.

In one embodiment of this invention there is provided a package for containing explosives. This package is comprised of an elongated housing having a chamber for receiving explosives and having a flared upper portion. A means is provided for holding a detonating cap in proximity to the chamber for receiving explosives. First and second conductor means are provided for making electrical connection with the detonation cap.

In another embodiment of this invention there is provided an explosive drilling tool for drilling a wellbore into subsurface formations. This drilling tool is comprised of an elongated housing having a fluid passageway therethrough and having a constriction in the lower portion of the passageway which forms a seat for receiving the flared portion of a package containing explosives. A spark pump is provided in the drilling tool for producing electrical energy when compressed by the increased pressure in the drill pipe resulting from the partial blocking of the drilling fluid passageway by the explosive package seating in the seating means. Electrodes electrically connected with the spark pump are provided for making electrical connection with the conductor means of the explosive package.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevation partly in cross section of a package containing explosives;

FIG. 2 is a cross-sectional elevation of a drilling tool located in a wellbore attached to a drill pipe and having a package containing explosives seated in a seating means; and

FIG. 3 illustrates this invention in the environment of a wellbore.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention involves new and improved combination rotary and explosive drilling methods and apparatus for drilling a wellbore into the earth formations. A wellbore normally is initiated and drilled into the earth by conventional rotary methods until a hard earth formation, which is expensive to drill, is reached. At this time the drill pipe is pulled from the wellbore and the rotary bit removed and replaced with the drilling tool of this invention. The drill pipe is then run back into the wellbore until the drilling tool reaches the bottom thereof. Drilling fluid is circulated down the drill pipe and up the annulus. An explosive charge contained in a package is inserted into the circulating drilling fluid and carried down the drill pipe until it seats in the drilling tool where it partially blocks the flow of drilling fluid and produces an increase in the pressure of the drilling fluid in the drill pipe. This increase in pressure compresses a spark pump contained in the housing of the drilling tool and produces electrical energy. This electrical energy is conducted to electrodes mounted in the drilling tool and detonates the explosive charge and fragments the earth formation below the drilling too. The drill pipe is rotated by conventional surface equipment to rotate the drilling tool and cutting means attached thereto to cut the wellbore to gauge. The fragmented earth formations are removed from the wellbore by the circulating drilling fluid.

For a better understanding of this invention, a more detailed description given with reference to the drawings follows. Referring specifically to FIG. 1, there is shown a package 2 for containing explosives to be injected down a drill pipe. This package 2 is comprised of an elongated housing 1 having a chamber 3 therein for containing explosives 5. Elongated housing 1 has a flared portion 7 for seating in the seating means of a drilling tool to be described later. Chamber 3 extends a sufficient distance below flared portion 7 to ensure that explosives 5 are positioned at least partially below a portion of a reflecting surface of the drilling tool when package 2 is seated in the drilling tool. There is provided a band 9, e.g. metal, and an indention in elongated housing I for holding a detonating cap 11 having leads l3 and 15 in proximity to chamber 3. A first conductor I7 is provided for making electrical connection with a first electrode in the drilling tool (FIG. 2). First conductor 17 is adapted for receiving lead 15.

Likewise, a second conductor 19 is provided for making electrical connection with a second electrode in the drilling tool (FIG. 2). Conductor 19 is also adapted for receiving lead 13.

Elongated housing 1 desirably is constructed of a frangible material, such as plastic or bakelite. The desirability for using a frangible material is twofold. First, upon detonating explosives 5 in chamber 3, elongated housing 1 is fragmented so that it may be removed from the wellbore by circulating drilling fluid. Second, having elongated housing I made of a frangible material allows the package 2 containing explosives to be removed from the drilling tool in the case of a misfire by applying a high hydrostatic pressure on the package. The high hydrostatic pressure causes the collapse of flared portion 7 and forces the package containing explosives out of the drilling tool where it is destroyed by later explosions or by the grinding action of the drilling tool.

Referring to FIG. 2, there is shown located in a wellbore 26 a drilling tool 21 attached by connection 23 to drill pipe 25. Drilling tool 21 is comprised of a housing 27 having a fluid passageway 29 therethrough which is in alignment with the fluid passageway 30 of drill pipe 25. There is a constriction in the lower portion of fluid passageway 29 which forms a seat 31 for the receiving of flared portion 7 of package 2, shown seated in seat 31 of drilling tool 21.

Housing 27 of drilling tool 21 has a chamber 36 therein in fluid communication with fluid passageway 29. The interior surfaces of the chamber are coated with an insulating material 34, e.g. ceramic. Piezoelectric means 33 are stacked in this chamber 36 to fonn a spark pump. An insulating washer 32 serves as a buffer between the lower end of drill pipe 25 and the upper piezoelectric means to contain the stacked piezoelectric means in the chamber. Appropriate piezoelectric means for use in this embodiment may typically be discs, cylinders, or rings made of lead zirconate-lead titanate ceramic. These piezoelectric means have the interior portion removed to form approximately a cylindrical passageway having the central axis of the passageway coinciding with the central axis of the piezoelectric means. The faces of the piezoelectric means are silvered and form condensers of rather high capacitance for their size.

When piezoelectric means 33 are compressed an electric potential develops between opposite silvered faces that is proportional to the applied pressure. This potential appears essentially instantaneously. Thus, a condition is developed where one silvered face of piezoelectric means 33 has a positive potential as compared to its opposite face. Piezoelectric means 33 are stacked in chamber 36 of housing 27 by a method of alternately inverting each during stacking so that positive faces contact one another and negative faces contact one another. The lower end of the column of piezoelectric means 33 is supported by a shoulder 35 of housing 27. Channels 37 and 39 are provided in housing 27 for housing electrical conductors 41 and 43 which are used to connect the piezoelectric means 33 in parallel. Conductors 41 and 43 are then connected through spark gaps 42 and 44 to electrodes 45 and 47 such that the electrical energy generated by the spark pump builds up to a sufficient voltage to are across spark gaps 42 and 44 and is conducted to the electrodes 45 and 47 for detonating the explosive charges.

When explosive package 2 seats in seat 31 of housing 27, the flow of drilling fluid through passageway 29 is partially blocked. This causes an increase in the drilling fluid pressure above explosive package 2 and compresses the spark pump comprised of piezoelectric means 33. The spark pump produces an electrical voltage which is connected through conductors 41 and 43 to electrodes 45 and 47. Conductors l7 and 19 are in electrical connection with electrodes 45 and 47 when explosive package 2 is seated in seat 31 and thus the electrical energy produced by the spark pump is conducted through leads I3 and 15 to detonating cap 11 and detonates the explosives contained in explosive package 2. The energy from the resulting explosion is concentrated by a concentrator 49 and fragments the earth formation at the bottom of the borehole. Drilling tool 21 is rotated, thereby rotating cutting means 51 about the bottom of the wellbore to cut the wellbore to gauge. Drilling fluid is circulated through fluid passageways 30 and 29 and back up the annulus, thereby removing the debris from the bottom of the wellbore.

For a better understanding of the method of this invention a detailed description is given with reference to FIG. 3. A wellbore 26, the lower portion of which is shown in FIG. 2, is initiated and drilled into the earth formations by conventional rotary techniques until a hard formation, which is expensive and difficult to drill, is reached. At this point, the drill pipe is pulled from the wellbore and the conventional rotary bit removed from the end thereof. The drilling tool 21 of this invention is then attached to the end of the drill pipe and lowered in the wellbore until it reaches the bottom thereof. Drilling fluid is circulated from a mud pit (not shown) through hose 61, explosive charge magazine 63, kelly 65, drill pipe 25, and up the annulus formed by the drill pipe and the wellbore and back to the mud pit. Explosive charges packaged as illustrated in FIG. 1 are inserted in the circulating drilling fluid and are carried down the drill pipe and seated in the seating means provided in the drilling tool. A conventional explosive charge magazine is used for inserting the explosive charges in the circulating drilling fluid. An example of such a magazine is illustrated in U.S. Pat. No. 3,0l4,423, to Robinson et al. When an explosive charge is seated in the seating means the flow of drilling fluid is restricted resulting in an increase in the pressure in the column of drilling fluid above the explosive charge. This pressure increase compresses the spark pump and forms electrical energy. The electrical energy from the spark pump is conducted to first and second electrodes located in the drilling tool and detonates the explosive charge, thus fragmenting the earth formations below the drilling tool. The drill pipe is rotated at the surface by conventional means to rotate the drilling tool and cutting means attached thereto, further fragmenting the earth formations and producing a wellbore of a desired gauge or minimum desired size. Subsequently other explosive charges are circulated down the drill pipe and exploded to further the drilling. Preferably the explosive charges are spaced about 50 to feet apart in the drill pipe so that drilling may be effected rapidly while not detonating subsequent charges in the drill pipe above the drilling tool. The drill pipe is lowered at a rate commensurate with the forming of new hole and the fragmented earth formations and debris are removed from the wellbore by the circulating drilling fluid.

A pressure-sensing device 67 is located in the circulating drilling fluid system in a position such that the pressure of the drilling fluid within the drill pipe may be measured. This pressure-sensing device is connected to a gauge normally positioned on the rig floor. Pressure fluctuations indicate when a charge seats in the drilling tool and when it is exploded. For example, when it seats in the drilling tool there is a pressure increase and when it explodes there is a sudden surge of pressure followed by a drop to the normal circulating pressure. Thus, the pressure fluctuations give an indication of the formation of new hole and serve as a guide in lowering the drill pipe at a rate commensurate with removal of fragmented earth formations from the wellbore.

In a preferred embodiment of this invention, the energy resulting from detonating explosive charges is concentrated to more efficiently utilize this energy in fragmenting the earth formations at the wellbore bottom. The explosives are positioned below the upper part of a concentrator and then detonated. The concentrator concentrates the energy to a focal region, thereby increasing the intensity of the energy in this region. By varying the location of the center of gravity of the explosives with respect to the concentrator, when the concentrator is an ellipsoidal reflector, the focusing effect is varied and the ellipsoidal reflector, the focusing effect is varied and the distribution of the concentrated energy is varied over the wellbore bottom. This phenomenon is beneficially used in drilling a wellbore by sequentially detonating explosives of different lengths, that is, explosives whose centers of gravity are at different locations below the concentrator. For example, a long explosive charge may be detonated first to form a relatively small hole. Thereafter, a short explosive charge, one having its center of gravity nearer the concentra tor, may then be detonated. The focusing effect of the short charge is reduced causing the energy to be distributed over a larger volume and causing the formation of a larger hole.

For a better understanding of these features of the invention, reference is made again to P16. 2 and particularly to the portion of FIG. 2 showing explosive charge 2 seated in seat 31 with explosives 5 being located below the upper part of a concentrator d9. A relatively long first explosive charge of a determined length is seated in seat 31 such that the center of the explosive charge is located at point 80. This first charge is detonated and the energy concentrated by being focused to focal point 81 with the result of forming a relatively narrow or small hole in the earth formation. After detonation of the first charge, a relatively short second explosive charge (not shown) of a determined length is then seated in seat 31 such that the center of this second explosive charge is positioned at point 82. The second explosive charge is detonated and the energy is focused at focal point 83 located below focal point 81. The focusing effect is thus reduced at the position of the wellbore bottom causing the energy to be distributed over a larger volume centered about focal point 83 and resulting in the formation of a large hole. This procedure may be repeated as desired in drilling the wellbore.

I claim:

1. A package for containing explosives to be injected along with fluid down a drill pipe located in a wellbore and adapted for seating in a drilling tool connected to the lower end of said drill pipe, comprising:

an elongated housing having a chamber therein adapted to receive said explosives:

a flared housing integral with an end of said elongated housing adapted for seating in said drilling tool and blocking the passage of said fluid down said drill pipe;

a first conductor means for making electrical connection with said drilling tool; and

a second conductor means spaced laterally from said first conductor means for making electrical connection with said drilling tool.

2. The package of claim 1 wherein said elongated housing is comprised of a frangible material 3. An explosive charge to be injected along with fluid down a drill pipe located in a wellbore and adapted for seating in a drilling tool, having two electrodes, connected to the lower end of said conduit, comprising:

an elongated housing having a chamber therein containing explosives, said elongated housing having a flared portion and a reduced portion extending below'said flared portron;

a detonating cap supported by said elongated housing having two leads in proximity to said explosives;

a first conductormeans for making electrical connection with an electrode in said drilling tool, said first conductor means being electrically connected to a lead of said detonating cap; and

a second conductor means for making electrical connection with the other electrode in said drilling tool, said second conductor means being electrically connected to the said electrode means. I 5. The explosive drilling tool of claim 4 wherein cutting means are provided on the lower portion of said housing for cutting said wellbore to gauge.

6. The explosive drilling tool of claim 5 wherein the lower portion of said housing is shaped to concentrate energy resulting from detonating explosives to drill a wellbore.

7. The explosive drilling tool of claim 6 wherein the lower portion of said housing is shaped in the form of an ellipsoidal reflector.

8. A method of drilling a wellbore through earth formations, comprising:

circulating a drilling fluid down a drill pipe located in said wellbore and up the annulus formed by said drill pipe and said wellbore;

circulating an explosive charge down said drill pipe;

seating said explosive charge at a location adjacent the lower end of said drill pipe to restrict the flow of drilling fluid through said drill pipe whereby the pressure within said drill pipe is increased;

producing electrical energy in response to the increase in said pressure;

applying said electrical energy to said explosive charge whereby said explosive is detonated to create explosive energy; and

concentrating said explosive energy to fragment said earth formations.

9. A combination rotary and explosive method of drilling a wellbore through earth formations, comprising:

circulating a drilling fluid down a drill pipe located in said wellbore and having a drill bit with cutting means and explosive seating means attached to the lower end thereof; circulating an explosive charge down said drill pipe; seating said explosive charge on said seating means to restrict the flow of drilling fluid through said drill pipe whereby the pressure within said drill pipe is increased;

producing electrical energy in response to the increase in said pressure;

applying said electrical energy to said explosive charge whereby said explosive is detonated to create explosive energy;

concentrating said explosive energy to fragment said earth formation; and

rotating said drill bit to cut said wellbore to gauge.

10. The method of claim 9 wherein there is sequentially circulated long an short explosive charges to fragment the wellbore bottom. 

2. The package of claim 1 wherein said elongated housing is comprised of a frangible material.
 3. An explosive charge to be injected along with fluid down a drill pipe located in a wellbore and adapted for seating in a drilling tool, having two electrodes, connected to the lower end of said conduit, comprising: an elongated housing having a chamber therein containing explosives, said elongated housing having a flared portion and a reduced portion extending below said flared portion; a detonating cap supported by said elongated housing having two leads in proximity to said explosives; a first conductor means for making electrical connection with an electrode in said drilling tool, said first conductor means being electrically connected to a lead of said detonating cap; and a second conductor means for making electrical connection with the other electrode in said drilling tool, said second conductor means being electrically connected to the other lead of said detonating cap.
 4. An explosive drilling tool for drilling a wellbore into subsurface formations, comprising: a housing having a fluid passageway therethrough; a constriction in the lower portion of said passageway forming a seat adapted to receive an explosive package for containing explosives; spark pump means for producing electrical energy in response to applied pressure, mounted in said housing in pressure communication with said fluid passageway; electrode means in the wall of said passageway; and means for electrically connecting said spark pump means to said electrode means.
 5. The explosive drilling tool of claim 4 wherein cutting means are provided on the lower portion of said housing for cutting said wellbore to gauge.
 6. The explosive drilling tool of claim 5 wherein the lower portion of said housing is shaped to concentrate energy resulting from detonating explosives to drill a wellbore.
 7. The explosive drilling tool of claim 6 wherein the lower portion of said housing is shaped in the form of an ellipsoidal reflector.
 8. A method of drilling a wellbore through earth formations, comprising: circulating a drilling fluid down a drill pipe located in said wellbore and up the annulus formed by said drill pipe and said wellbore; circulating an explosive charge down said drill pipe; seating said explosive charge at a location adjacent the lower end of said drill pipe to restrict the flow of drilling fluid through said drill pipe whereby the pressure within said drill pipe is increased; producing electrical energy in response to the increase in said pressure; applying said electrical energy to said explosive charge whereby said explosive is detonated to create explosive energy; and concentrating said explosive energy to fragment said earth formations.
 9. A combination rotary and explosive method of drilling a wellbore through earth formations, comprising: circulating a drilling fluid down a drill pipe located in said wellbore and having a drill bit with cutting means and explosive seating means attached to the lower end thereof; circulating an explosive charge down said drill pipe; seating said explosive charge on said seating means to restrict the flow of drilling Fluid through said drill pipe whereby the pressure within said drill pipe is increased; producing electrical energy in response to the increase in said pressure; applying said electrical energy to said explosive charge whereby said explosive is detonated to create explosive energy; concentrating said explosive energy to fragment said earth formation; and rotating said drill bit to cut said wellbore to gauge.
 10. The method of claim 9 wherein there is sequentially circulated long an short explosive charges to fragment the wellbore bottom. 